Communication systems are widely used in computer and device networks to communicate information between computers and other electronic devices. Transceivers of a communication system send and receive data over a communication link (including one or more channels) of a communication network to communicate with other transceivers. A transceiver includes a transmitter for sending information across a link, and a receiver for receiving information from a link. The receiver detects transmitted data on the link and converts the data into a form usable by the system connected to the transceiver. For example, one widely-used network communication standard is Ethernet which includes several different standards for different network bandwidths, including 10GBASE-T allowing 10 gigabit/second connections over unshielded or shielded twisted pair cables.
There are many blocks in a typical receiver of a communication system which must operate near an optimal operating point in order that there be robust detection of data transmitted on a communication link. The optimal operating point is usually determined through an initial training process in which the far-end transmitter sends a known training signal and the receiver optimizes its own parameters using the training signal and a training method. Some of the receiver blocks that require training are the receiver gain block, equalizers (both feed-forward and feedback), echo and cross-talk cancellers, and timing recovery. The training methods typically find the optimal receiver parameters by minimizing some measure of error. The error is usually identified as the difference of the known transmit data and the received data decoded by the receiver.
In addition to the initial training period, the receiver has to update its parameters constantly to track the changes in the communication link as well as the noise sources. In some communication systems, the transmitters re-send the training sequence periodically in predefined intervals to provide the far-end receiver opportunities to adapt to the new channel and noise conditions. In other communication systems, where the communication channels and noise sources change slowly, the adaptation may be done without any interruption in data transmission. In such systems, the mismatch between the current and the optimal receiver settings are assumed to be sufficiently small such that the receiver decodes the transmit data correctly with high probability. With that assumption, the decoded data can be used in lieu of the training signal to calculate the error signal, which in turn is used for parameter optimization. This method of parameter update is often referred to as “decision-directed” because the error signal is derived from the decisions that the receiver makes to decode the transmitted data.
A decision-directed update method relies on the fundamental assumption that the receiver mostly decodes the data correctly. This is true only when the rate of changes in the channels and noise sources is sufficiently slower than the update rate of the receiver parameters. Under this condition, the receiver operating point never deviates significantly from the optimal point. If this condition is not met, then the estimated error signal calculated from the decoded data may not be a good representative of the real error signal. This may cause the update method to choose parameters that are far from optimal, and these non-optimal receiver settings will in turn cause further error in the decoded data. This creates a positive feedback that deteriorates the receiver operation very quickly and usually results in the failure of the communication link. Once the link has failed, the transceivers must go through a full training sequence to reestablish the link, which is a fairly long process, and requires processing time and resources which often are not fully needed to reestablish the link.
Accordingly, what is needed are systems and methods that allow for less time in retraining transceiver parameters after deterioration or failure of a communication link in a communication system.